For technologies whereby a straightening grid is disposed on an upstream side of an AFM that measures a flow rate of intake air suctioned into an engine (internal combustion engine that generates rotative power as a result of combustion of fuel) in an air flow direction, JP-A-H06-026903, and JP-A-H07-071985 corresponding to U.S. Pat. No. 5,253,517 will be described below. According to the technology described in JP-A-H06-026903, the straightening grid is disposed on the upstream side of the AFM in the air flow direction, and an airflow inhibition member for preventing a direct inflow of air into the air inlet (flat plate perpendicular to the air flow direction) is disposed on an upstream side of an air inlet of the AFM in the air flow direction.
This straightening grid of JP-A-H06-026903 is configured through the combination of many cross shapes. There is an increased pressure loss of the straightening grid obtained by combining together many crosses in this manner in accordance with the increase in the number of crosses. Moreover, a turbulent flow is more easily produced on a downstream side of the straightening grid obtained by the combination of many crosses as the number of crosses increases. Accordingly, a signal fluctuation of the AFM is increased due to the turbulent flow. Furthermore, by the straightening grid of the combination of many crosses, a deviation of a flow speed produced in a duct cannot be averaged.
In the technology in JP-A-H06-026903, the airflow inhibition member is disposed on the upstream side of the air inlet of the AFM in the air flow direction. Consequently, the turbulent flow is generated immediately downstream of the airflow inhibition member to cause the increase in the signal fluctuation of the AFM.
According to the technology described in JP-A-H07-071985, similar to JP-A-H06-026903, the straightening grid is disposed on the upstream side of the AFM in the air flow direction. This straightening grid of JP-A-H07-071985 is configured by combining together many cross shapes similar to JP-A-H06-026903. For this reason, similar to the defects of the technology in JP-A-H06-026903, the pressure loss of the straightening grid increases in accordance with the increase in the number of crosses; a turbulent flow is more easily produced on a downstream side of the straightening grid as the number of crosses increases, to cause an increase of a signal fluctuation of the AFM; and a deviation of a flow speed produced in a duct cannot be averaged.